550 



leaves, approximately in the centre or somewhat below it. The places of 

 breaking were flatly compressed and began at once to become flabby. The 

 tips of the leaflets, which otherwise did not appear wilted, were flabby on 

 the broken leaves and began to turn brown. 



Since such a breaking of the ])etioles had not been observed previously, 

 this i)lant was again placed out of doors on the niglit of the 2i-22d of 

 March. The temperature fell to 7 degrees C. below zero and the next 

 morning the leaflets of all the leaves hung downward at a sharp angle. The 

 youngest leaves showed this ])henomenon the least of all. Even in a still 

 frozen condition, no part of the young growth seemed brittle, or of a glassy 

 consistency, so that any conclusion as to a formation of ice crusts in the 

 tissue was scarcely possible. Tlie leaflets were soft and flal)by, of a grayish 

 green color, and the petioles, as long as the ])lant stood out of doors, cur\ed 

 downward sharply but were not broken. The breaking took place only 

 after some hours indoors and, indeed, as in the first observed injur)', near 

 the middle of the petiole. This place shrivelled at once and turned brown. 

 At the same time all the leaflets, with the exception of the youngest, began 

 to turn black, starting at their ])lacc of insertion, and the tii)s curled ui)ward 

 and became dry. 



The processes of breaking must be traced back to a lever action con- 

 nected with decreased turgidity, for, as soon as some of the leaves, broken 

 by weak frost action, were removed and placed in water, they lost the ap- 

 pearance of wilting in spite of the liroken place, and a great stifi^ness of the 

 tissues set in. To be sure, the leaflets retained their downward inclination, 

 peculiar to the youthful stage, but their intercostal fields curved outward 

 strongly between the veins and their side edges began to turn under. 



The wilting and breaking is explained by the inner phenomenon of 

 cleavage in the pith body of the petioles. In the chestnut the petiole has a 

 structure similar to the trunk, inasmuch as it possesses a closed circle of 

 vascular bundles which completely and uniformly surrounds the broad, 

 colorless pith disc and passes over into it in a gradation similar to the pith 

 crown. Even after the weakest frost action it was noticed that the pith 

 body of the petioles which had not yet broken, contained holes, usually of a 

 radial arrangement, and seemed ready to break, because of the limpness of 

 the corresponding place. This occurred near the base of the petiole. Be- 

 cause the vascular body, running through the centre of the pith disc and 

 consisting of two or three bundles, remained intact and the tears in the pith 

 parenchyma ran radially to all sides, a peculiar star-like figure of cleavage 

 was sometimes found. In the leaves, which had been broken only after a 

 second, stronger frost action, the splitting of the pith disc at times was so 

 strong that the central vascular bundle cord was connected with the peri- 

 pheral vascular bundles only by a slender parenchyma strip and all the rest 

 of the pith disc had been dissolved. The holes were continued, not infre- 

 quently, in or between the peripheral vascular bundles and formed splits 

 which extended to the edge. Within these occurred also tangential out- 



